GeometricNetwork基本概念和连接规则..doc

Geometric Network 基本概念和连接规则 Geometric Networks（几何网络）可以在ArcInfo和ArcEditor中创建，ArcView只能浏览。Geometric Networks一般用于自来水管道流向、电线、燃气管道、电话网络等，它由一组相互连接的edges和junctions组成，并且具备相应的连接规则来代表真实世界中相应实体的行为。Geodatabase feature classes作为数据源用以定义geometric network。几何网络一般建立于geodatabase的feature dataset中，feature dataset存储的是几何网络的edges和junctions数据源，几何网络的两个主要组成部分就是Edges和Junctions。下面是对这些基本要素的定义：Edges - An edge is a feature which has a length through which some commodity flows. Edges are created from line feature classes in a feature dataset and correspond to edge elements in a logical network. Examples of edges: water mains, electrical transmission lines, gas pipelines, telephone lines, etc... Junctions - A junction is a feature that allows two or more edges to connect and facilitates the transfer of flow between edges. Junctions are created from point feature classes in a feature dataset and correspond to junction elements in the logical network. Examples of junctions: fuses, switches, service taps, valves, etc...几何网络中的Edges和Junctions在拓扑关系上是相互连接的，edges必须通过junctions和其他edges连接。关于edges和junctions有更细的划分：There are two types of edges in a geometric network: Simple Edges - Simple edges are always connected to exactly two junctions, one at each end. An example of a simple edge would be a water lateral in a water network. The water lateral connects at one end to a junction along the main distribution line and, at the other end, to a service point junction (such as a tap or pump). Simple edges have no mid-span connectivity. If a new junction is snapped mid-span on a simple edge, thereby establishing connectivity, then that simple edge is physically split into two features. A simple edge corresponds to a single edge element in the logical network. Complex Edges - Complex edges are always connected to at least two junctions at their endpoints but can be connected to additional junctions along their length. An example of a complex edge would be a water main in a water network. Th